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Protractors

Navigation

As noted in the Introduction, the earliest use of protractors was probably in navigation. Protractors assisted with laying out angles to indicate the actual or desired direction of a ship. Makers might have also marked protractors with additional scales to be employed in computing a ship’s speed or direction, such as rhumbs or seconds. When coastal surveying projects were conducted in the 19th century, navigators used substantial protracting instruments called station pointers both to ascertain their position along a coastline and to record the topographical measurements of that coastline. In the 20th century, protractors were also utilized in aviation navigation.

This clear Perspex (acrylic glass) square protractor is divided by single degrees and marked by tens in the clockwise direction from 010° to 350°. A red arrow points to the origin. The marks for 090°, 180°, and 270° are replaced by the compass points E, S, and W, respectively. Diagonal lines to the four corners of the protractor are marked with the compass points NE, SE, SW, and NW. A pinhole is at the center of the protractor.

The interior of the protractor is marked with a grid. Tick marks (four per square) appear along the X and Y axes and around the outside edge of the grid. The top is labeled (in red): MACLEAN PROTRACTOR. Maker's marks are at the bottom: REGD. TRADE MK. AIRNAVA; J. D. MACLEAN ∙ Co. LONDON W.C.2. The protractor is stored in a tan cardboard case, which is printed with instructions for using the instrument. Marine and aviation navigators could employ it as a parallel rule, station pointer, and plotter. John Donald Maclean patented a rectangular protractor and parallel rule in the United States. No record of a trademark for "Airnava" was found in the United States or in Great Britain. This form of protractor is standard and is sometimes called a Douglas type of square protractor. Weems & Plath manufactures similar protractors in the 21st century.